Polyarylene thioethers including polyphenylene thioether have heretofore been prepared by condensation polymerization of an aromatic dihalide and an alkali metal sulfide in a polar solvent at a high temperature under pressure.
This condensation polymerization has, however, such problems that (i) an alkali metal salt remains in polyarylene thioether and deteriorates its electrical properties and (ii) this production cost is high because a great amount of energy is consumed due to carrying out polymerization at a high temperature under pressure.
A process in which thiophenol monomer is polymerized in the presence of a catalyst such as MoCl.sub.5 /CF.sub.3 COOH is disclosed in USSR Patent No. 698,988. However, the product resulting from that process is poly(arylene thiol), and the process is not advantageous in industrial use since the catalyst used is expensive.
Furthermore, another process using sulfuric acid as a catalyst is known, but said process has such a disadvantage that much by-products and a considerable amount of cross-linked polymers are produced.
Processes for preparing polyarylene thioethers using diphenyldisulfide and/or thiophenol have been disclosed also in Japanese Patent Application Laid-Open Nos. 213526/1988 and 213527/1988, but they have the problems that expensive Lewis acids and oxidizing agents must be used in large amounts.
The present invention was accomplished under above circumstances, and the object of it is to dissolve the problems mentioned above, and to provide a process, which is greatly advantageous in industrial use, for producing a polyarylene thioether having excellent electric, mechanical and chemical properties, particularly a substantially straight-chain polyarylene thioether with little by-production of cross-linked polymers, with a simple and easy procedure, under mild polymerization conditions, and at a low cost.